Method for identifying inner curtain structure of fault control fracture-vug type reservoir

Abstract

The invention belongs to the technical field of oil exploration and development, and relates to a fault control fracture-cavity type reservoir inner curtain structure identification method. According to the method, the fault control fracture-vuggy reservoir is divided into different inner curtain structures, a numerical simulation method is adopted to construct a change chart of stress-strain curves in rock mechanical properties based on the different inner curtain structures of the fault control fracture-vuggy reservoir, and the inner curtain structures of the reservoir are judged by monitoring the stress-strain curves of the reservoir and projecting the stress-strain curves into the chart. According to the method, the limit range chart is drawn based on the change of the stress-strain curve in the rock mechanical property, a new method is provided for identifying the inner curtain structure of the fault control fracture-cavity type reservoir, the heterogeneity of the reservoir can be effectively represented, errors caused by the technical detection aspect are reduced, the pertinence is high, and the operation is simple and convenient.

Description

Technical Field

[0001] The present invention relates to the technical field of petroleum exploration and development, and in particular to a method for identifying the internal structure of a fault-controlled fracture-cavity reservoir. Background Art

[0002] Fault-controlled fracture-vuggy reservoirs are an important type of carbonate reservoir. Their reservoir space is dominated by a network of dissolution pores and fractures controlled by fault zones, exhibiting strong heterogeneity and a complex spatial structure. Under the multi-stage structural fragmentation of major faults, these reservoirs form numerous branching and secondary fractures that have been expanded by dissolution, forming a vast fracture network system that serves as a favorable pathway for oil and gas migration, injection, and accumulation.

[0003] With the acquisition of high-precision seismic data and the development of computer technology, the requirements for identifying the internal structure of fracture-vuggy reservoirs are becoming increasingly demanding. In fault-controlled fracture-vuggy reservoirs, rocks can be divided into a central fracture zone (fault core), a fracture zone surrounding the fracture zone (fault breccia zone and fracture reservoir), and an external matrix rock zone (surrounding rock zone) based on the location of the fault zone. Due to the unique geomechanical properties of fault-controlled fracture-vuggy reservoirs, the fracture zone exhibits significant rock discontinuity, and the rock mechanical properties of different zones transitioning from the fracture zone to the matrix zone vary significantly.

[0004] At present, the identification of internal structures is mostly based on seismic data and well logging data. However, due to the limited accuracy of seismic and well logging technology, certain measurement accuracy errors occur.

[0005] Chinese patent number CN116931070A, "A Method for Characterizing Fault-Controlled Fracture-Vuggy Reservoirs," discloses a method for characterizing fault-controlled fracture-vuggy reservoirs. This method, based on inversion, introduces constraints to effectively reduce the spatial heterogeneity of the inversion results. It also provides optimization methods for suppressing background trends and enhancing abnormal responses, improving the accuracy of identifying dissolution vugs and fracture-vuggy zones.

[0006] The Chinese patent, CN119272461A, "Prediction Method, System, and Electronic Device for Fault-Controlled, Fracture-Vuggy High-Quality Carbonate Reservoirs," provides a method, system, and electronic device for predicting fault-controlled, fracture-vuggy high-quality carbonate reservoirs. Based on an introduced mathematical probability model, the system combines geophysical exploration techniques with mathematical analysis to quantitatively characterize and predict fault-controlled, fracture-vuggy high-quality reservoirs. The streamlined and rapid process enables accurate prediction of high-quality fracture-vuggy reservoirs, such as cavernous reservoirs.

[0007] Chinese patent number CN116299664A, "Method, device, and apparatus for determining reservoir volume in fault-controlled fracture-vuggy reservoirs," provides a method, device, and apparatus for determining reservoir volume in fault-controlled fracture-vuggy reservoirs. This method utilizes a self-organizing neural network model to comprehensively represent different seismic attribute information reflecting the seismic facies of fault-developed areas into an attribute data volume that effectively represents reservoir structure. This allows for quantitative characterization of different reservoir types using seismic facies.

[0008] The above patents focus on a relatively single type of identification of the internal structure of fault-controlled fracture-cavity reservoirs and do not consider conducting research based on rock mechanical properties as a breakthrough point. Summary of the Invention

[0009] This invention aims to provide a method for identifying the internal structure of fault-controlled fracture-vuggy reservoirs. Starting from the rock mechanical properties, it aims to solve the problem of identifying the internal structure type of fault-controlled fracture-vuggy reservoirs. This invention uses numerical simulation methods to construct a stress-strain curve chart based on the rock mechanical properties of different internal structures of fault-controlled fracture-vuggy reservoirs. By monitoring the reservoir's stress-strain curve and projecting it onto the chart, the internal structure of the reservoir can be determined, providing a new method for identifying the internal structure of fault-controlled fracture-vuggy reservoirs.

[0010] To achieve the above-mentioned purpose, the present invention adopts the following technical solution: a method and system for identifying the internal structure of a fault-controlled fracture-cavity reservoir, comprising the following steps:

[0011] (1) Obtain geological and physical data of the target fault-controlled fracture-cavity reservoir, including reservoir pressure, rock Young's modulus, rock Poisson's ratio and other parameters.

[0012] (2) According to the reservoir space characteristics of fault-controlled fracture-cavity reservoirs, the internal structure of fault-controlled fracture-cavity reservoirs is divided into three internal structure types, including fault type, fracture-cavity type and pore-fracture type.

[0013] (3) Based on the three types of internal structures, three mechanism models of internal structures are constructed, that is, numerical simulation mechanism models of fault-controlled fracture-cavity reservoirs with fault-type, fracture-cavity and pore-fracture-type internal structures are constructed.

[0014] (4) Based on the constructed mechanism models of different inner structures, under the action of the solid mechanics physical field, the stress-strain curve results of the mechanism models of different inner structures at different pressure levels are simulated and calculated;

[0015] Among them, the constitutive equation of the solid mechanics physical field in three dimensions can be expressed as:

[0016] σ xx =λe+2με xx ,σ yy =λe+2μεyy ,σ zz =λe+2με zz

[0017] τ xy =μγ xy , τ yz =μγ yz ,τ zx =μγ zx

[0018]

[0019] Where σ xx , σ yy , σ zz is the normal stress component, Pa; τ xy , τ yz , τ zx is the shear stress component, Pa; ε xx , ε yy , ε zz is the normal strain component, dimensionless; γ xy , γ yz , γ zx is the shear strain component, dimensionless; λ is the first Lame constant, GPa; μ is the second Lame constant, GPa; e = ε xx +ε yy +ε zz ; σ is stress, Pa; ε is strain, dimensionless.

[0020] The relationship between the first and second Lame constants and Young's modulus and Poisson's ratio is:

[0021]

[0022] Where E is Young's modulus, GPa; ν is Poisson's ratio, dimensionless.

[0023] (5) Draw the stress-strain curve results of the mechanism model with different internal structures and the stress-strain limit range chart in the same coordinate system;

[0024] (6) monitoring the stress and strain of the target reservoir to obtain the stress and strain curve of the target reservoir;

[0025] (7) Compare the stress-strain curve of the target reservoir in step (6) with the stress-strain boundary range map to clarify the corresponding type of the internal structure of the target reservoir.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] (1) Existing technologies mostly rely on single attributes (such as seismic amplitude) or general classifications (such as cave / fracture dichotomy), resulting in insufficient description of heterogeneity. The present invention proposes three internal structure classifications for fault-controlled fracture-cavity oil and gas reservoirs, which can effectively characterize reservoir heterogeneity and provide a reference for clarifying reservoir structure and optimizing oil and gas field well network deployment.

[0028] (2) The present invention proposes a new method to reflect the internal structure of fault-controlled fracture-cavity reservoirs by using the stress-strain variation curve in rock mechanics parameters. The internal structure type of fault-controlled fracture-cavity reservoirs is determined by the differences in rock mechanics properties of different internal structures. Starting from the properties of the reservoir rock itself, the method can effectively reduce the errors caused by technical detection, and is highly targeted and easy to operate.

[0029] (3) Compared with the existing technology, the present invention is more convenient. It can identify the internal structure of strata at different depths and pressures by constructing a map for the target fault-controlled fracture-cavity oil and gas reservoir once. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a reservoir numerical simulation model of the interrupted fracture type, fracture-cavity type and pore-fracture type internal structure of the present invention.

[0031] Figure 2 This is the reservoir stress-strain curve at 6200m in the G oil and gas reservoir in the embodiment.

[0032] Figure 3 This is a diagram showing the stress and strain limit range in the examples.

[0033] Figure 4 This is the sample core taken at 6200m from the G oil and gas reservoir in the embodiment.

[0034] Figure 5 These are the stress-strain curve results of some models in the examples at certain pressure levels. DETAILED DESCRIPTION

[0035] Based on geological data and well logging analysis, the G reservoir is a fault-controlled, fracture-vuggy carbonate reservoir located at a depth of 6,000 to 6,500 meters. This reservoir is dominated by a network of dissolution pores and fractures controlled by fault zones, exhibiting strong heterogeneity and a complex spatial structure. Well logging data and rock mechanics testing indicate that the reservoir pressure at 6,200 meters in the study area is 85 MPa, the Young's modulus is 28 GPa, and the Poisson's ratio is 0.27.

[0036] Based on the above analysis results, the internal structure of the reservoir of G fault-controlled fracture-cavity oil and gas reservoir was identified. The specific steps are as follows:

[0037] Step 1: Obtain geological and physical property data of the target fault-controlled fracture-cavity reservoir, with a reservoir pressure of 85 MPa, a Young's modulus of 28 GPa, and a Poisson's ratio of 0.27.

[0038] Step 2: Based on the reservoir space characteristics of fault-controlled fracture-cavity reservoirs, the internal structure of fault-controlled fracture-cavity reservoirs is divided into three categories, including fault-fracture type, fracture-cavity type and pore-fracture type.

[0039] The internal structures of fault-controlled fracture-vuggy reservoirs are divided into three categories, based primarily on the genetic mechanisms and spatial characteristics of the reservoirs: fault-dominated (fault-fracture type), dissolution-fracture composite (fracture-vuggy type), and pore-fracture type (pore-fracture type). This classification of internal structures can quantify reservoir heterogeneity and guide differentiated development strategies (such as deploying horizontal wells along fault zones for fault-fracture types, optimizing gas injection and gravity flooding for fracture-vuggy types, and implementing acid fracturing for pore-fracture types), significantly improving reservoir prediction accuracy and supporting the precise tapping of remaining oil potential.

[0040] Step 3: Based on the three types of internal structures, a numerical simulation model of fault-controlled fracture-cavity reservoirs with fault-type, fracture-cavity and pore-fracture-type internal structures is constructed.

[0041] The three types of internal structural fault-controlled fracture-cavity reservoir models all use discrete fracture networks for both fractures and cracks, providing a more realistic representation of fractures. The discrete fracture networks are programmed using MATLAB software to obtain discrete fracture models within a given range. The fault-fracture model includes both fractures and cracks. The fracture length range is set to 200m to 250m, the number of fractures is set to 4, the fracture length range is set to 40m to 60m, and the number of fractures is set to 36. The fracture-cavity model includes both fractures and caves. The fracture length range is set to 40m to 60m, the number of fractures is set to 32, and the caves are constructed using artificial geometric models. The diameter range is set to 20m to 70m, and the number of caves is set to 5. The pore-fracture model includes both porous matrix and fractures. The pores are set as a porous matrix with a porosity of 0.3. The fracture length range is set to 40m to 60m, and the number of fractures is set to 45. Based on the above-given crack length range, cave diameter range and generated number, three types of crack models are obtained respectively, thereby constructing three types of inside structure numerical simulation models.

[0042] Step 4: Based on the constructed numerical simulation models of different inner structures, under the action of solid mechanics physical field, simulate and calculate the stress-strain curve results of the numerical simulation model under the pressure level of 60MPa to 100MPa, such as Figure 5 .

[0043] Among them, the constitutive equation of the solid mechanics physical field in three dimensions can be expressed as:

[0044] σ xx =λe+2με xx ,σ yy =λe+2με yy ,σ zz =λe+2με zz

[0045] τ xy =μγ xy , τ yz =μγ yz ,τ zx =μγ zx

[0046]

[0047] Where σ xx , σ yy , σ zz is the normal stress component, Pa; τ xy , τ yz , τ zx is the shear stress component, Pa; ε xx , ε yy , ε zz is the normal strain component, dimensionless; γ xy , γ yz , γ zx is the shear strain component, dimensionless; λ is the first Lame constant, GPa; μ is the second Lame constant, GPa; e = ε xx +ε yy +ε zz ; σ is stress, Pa; ε is strain, dimensionless.

[0048] The relationship between the first and second Lame constants and Young's modulus and Poisson's ratio is:

[0049]

[0050] Where E is Young's modulus, which is 28 GPa, and ν is Poisson's ratio, which is 0.27. Calculation yields λ as 12.941 GPa and μ as 11.024 GPa.

[0051] Step 5: Under the action of solid mechanics physical field, simulate and calculate the stress-strain curve results of the numerical simulation model under the pressure level of 60MPa to 100MPa, and draw the stress-strain limit range chart of the fault-controlled fracture-cavity reservoir stress-strain curve results of the fault-type, fracture-cavity type and pore-fracture type internal structure in the same coordinate system, such as Figure 3 .

[0052] Step 6: Import the stress-strain curve chart into the reservoir stress-strain monitoring system, and use the reservoir stress-strain monitoring system to monitor the stress and strain at 6200m of the G oil and gas reservoir to obtain the reservoir stress-strain curve ( Figure 2 ).

[0053] The reservoir stress and strain monitoring system of the present invention may adopt a monitoring system commonly used in the art.

[0054] Step 7: Compare the stress-strain curve of the monitored target reservoir with the imported stress-strain curve chart of the fault-controlled fracture-cavity reservoir with different internal structures, so as to determine that the corresponding type of the internal structure at 6200m of the monitored target block reservoir is a pore-fracture reservoir ( Figure 3 ).

[0055] In order to verify the correctness of the above invention, core sampling was carried out at 6200m of G oil and gas reservoir ( Figure 4 ).

[0056] The sampled core clearly revealed cracks in the carbonate rock, and the core was intact, indicating the absence of fractures or caves. Furthermore, the core was carbonate rock, inherently a porous medium, indicating that the reservoir at 6200 m was a porous-fracture reservoir. This result was consistent with the results obtained in Step 7, demonstrating the validity of the inventive method.

[0057] The above description is merely an illustrative embodiment of the present invention and is not intended to limit the scope of the present invention. The implementation steps and related parameters are subject to change. Any equivalent changes and modifications made without departing from the technical solution of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A method for identifying the internal structure of a fault-controlled fracture-cavity reservoir, characterized in that: The fault-controlled fracture-cavity reservoir is divided into different internal structures. A numerical simulation method is used to construct a stress-strain curve change chart based on the different internal structures of the fault-controlled fracture-cavity reservoir in the rock mechanical properties. By monitoring the stress-strain curve of the reservoir and projecting it onto the chart, the internal structure of the reservoir can be determined.

2. The method for identifying internal structures of fault-controlled fracture-cavity reservoirs according to claim 1, characterized in that: The following steps are involved: (1) Obtain geological and physical property data of the target fault-controlled fracture-cavity reservoir; (2) According to the spatial characteristics of the reservoir body of the fault-controlled fracture-vuggy reservoir, the internal structure of the fault-controlled fracture-vuggy reservoir is divided into three types of internal structures; (3) Based on the three types of inner structures, numerical simulation models of three inner structures are constructed; (4) Based on the constructed numerical simulation models of different inner structures, under the action of the solid mechanics physical field, the stress-strain curve results of the numerical simulation models of different inner structures at different pressure levels are simulated and calculated; (5) Draw the stress-strain curve results of the mechanism model with different internal structures and the stress-strain limit range chart in the same coordinate system; (6) monitoring the stress and strain of the target reservoir to obtain the stress and strain curve of the target reservoir; (7) Compare the stress-strain curve of the target reservoir in step (6) with the stress-strain boundary range map to clarify the corresponding type of the internal structure of the target reservoir.

3. The method for identifying internal structures of fault-controlled fracture-cavity reservoirs according to claim 1, characterized in that: In step (2), the three types include fracture type, hole type and hole type.

4. The method for identifying internal structures of fault-controlled fracture-cavity reservoirs according to claim 1, characterized in that: In step (4), the constitutive equation of the solid mechanics physical field in three dimensions can be expressed as: s xx =λe+2with xx ,s yy =λe+2with yy ,s zz =λe+2with zz t xy =μγ xy ,t yz =μγ yz ,t zx =μγ zx Where σ xx , σ yy , σ zz is the normal stress component, Pa; τ xy , τ yz , τ zx is the shear stress component, Pa; ε xx , ε yy , ε zz is the normal strain component, dimensionless; γ xy , γ yz , γ zx is the shear strain component, dimensionless; λ is the first Lame constant, GPa; μ is the second Lame constant, GPa; e = ε xx +ε yy +ε zz ; σ is stress, Pa; ε is strain, dimensionless.

5. The method for identifying internal structure of fault-controlled fracture-cavity reservoir according to claim 4, characterized in that: In step (4), the relationship between the first Lame constant and the second Lame constant and Young's modulus and Poisson's ratio is: Where E is Young's modulus, GPa; ν is Poisson's ratio, dimensionless.

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